Wireless relays are infrastructure devices intended for either increasing the user experience in intra-cell coverage holes or for extending the cell coverage. For mobile wireless applications, a complete standardized solution was provided by WiMAX (IEEE802.16-2009) while 3GPP LTE provided a solution (TS 36.116) not pursued commercially. These solutions were particularly designed for their specific RAN solutions.
While the lower frequency bands (≤5 GHz) exhibit better NLOS propagation performance, the poorer diffraction spread for cm/mm waves (≥20 GHz) causes much higher propagation losses in NLOS scenarios than the lower bands. Since this confines the use cases for cm/mm bands to mostly LOS propagation cases, providing additional intra or extra cell coverage requires to specifying dedicated multi-hop radio relays for the ≥20 GHz bands.